Improve type safety for persona loading error tracking

[dlqqq]

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In PR #1397, we introduced error tracking for persona loading failures using untyped dictionaries. This reduces type safety compared to the previous typed implementation. We should replace the dictionary approach with a proper dataclass to improve type safety and IDE support.

Additional improvements:

• Add ClassVar annotation to _ep_persona_classes since it's shared across instances
• Remove unused line 202: item.get("module") which fetches but doesn't use the value